U.S. patent application number 11/625553 was filed with the patent office on 2007-07-19 for support apparatus for microphone diaphragm.
This patent application is currently assigned to ANALOG DEVICES, INC.. Invention is credited to Jason W. Weigold.
Application Number | 20070165888 11/625553 |
Document ID | / |
Family ID | 38263209 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070165888 |
Kind Code |
A1 |
Weigold; Jason W. |
July 19, 2007 |
Support Apparatus for Microphone Diaphragm
Abstract
A microphone includes a diaphragm assembly supported by a
substrate. The diaphragm assembly includes at least one carrier, a
diaphragm, and at least one spring coupling the diaphragm to the at
least one carrier such that the diaphragm is spaced from the at
least one carrier. An insulator (or separate insulators) between
the substrate and the at least one carrier electrically isolates
the diaphragm and the substrate.
Inventors: |
Weigold; Jason W.;
(Somerville, MA) |
Correspondence
Address: |
BROMBERG & SUNSTEIN LLP
125 SUMMER STREET
BOSTON
MA
02110-1618
US
|
Assignee: |
ANALOG DEVICES, INC.
One Technology Way
Norwood
MA
02062-9106
|
Family ID: |
38263209 |
Appl. No.: |
11/625553 |
Filed: |
January 22, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11113925 |
Apr 25, 2005 |
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11625553 |
Jan 22, 2007 |
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11366941 |
Mar 2, 2006 |
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11625553 |
Jan 22, 2007 |
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60708449 |
Aug 16, 2005 |
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60760854 |
Jan 20, 2006 |
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Current U.S.
Class: |
381/174 |
Current CPC
Class: |
H04R 19/005 20130101;
B81B 2203/0307 20130101; H04R 2499/11 20130101; H04R 2410/00
20130101; B81B 2203/0127 20130101; H04R 2307/201 20130101; H04R
7/20 20130101; B81B 3/0072 20130101; B81B 2201/0257 20130101; B81B
3/0037 20130101 |
Class at
Publication: |
381/174 |
International
Class: |
H04R 25/00 20060101
H04R025/00 |
Claims
1. A microphone comprising: a substrate; a diaphragm assembly
supported by the substrate, the diaphragm assembly including at
least one carrier, a diaphragm, and at least one spring coupling
the diaphragm to the at least one carrier, the diaphragm being
spaced from the at least one carrier; and at least one insulator
between the substrate and the at least one carrier so as to
electrically isolate the diaphragm and the substrate.
2. A microphone according to claim 1, wherein the substrate and the
diaphragm are capacitively coupled to form a fixed plate and a
movable plate of a variable capacitor.
3. A microphone according to claim 1, wherein each carrier is
coupled to an insulator and wherein such insulator is coupled to
the substrate.
4. A microphone according to claim 1, wherein the diaphragm is
perforated.
5. A microphone according to claim 1, wherein the diaphragm is
corrugated.
6. A microphone according to claim 1, wherein the diaphragm has a
plane when unflexed, the at least one spring producing a space
between the diaphragm and the at least one carrier in the direction
of the plane of the diaphragm.
7. A microphone according to claim 1, wherein the diaphragm is
stress isolated from the at least one carrier.
8. A microphone according to claim 1, wherein the at least one
carrier comprises a single unitary carrier surrounding the
diaphragm.
9. A microphone according to claim 1, wherein the at least one
carrier comprises a plurality of distinct carriers.
10. A microphone according to claim 1, wherein the at least one
insulator comprises an oxide.
11. A microphone according to claim 1, wherein the diaphragm
assembly comprises polysilicon.
12. A microphone according to claim 1, wherein the at least one
insulator is formed directly or indirectly on the substrate.
13. A microphone according to claim 12, wherein the at least one
carrier is formed directly or indirectly on the at least one
insulator.
14. A microphone according to claim 1, wherein the substrate is
formed from a silicon layer of a silicon-on-insulator wafer.
15. A microphone according to claim 1, wherein the substrate
includes a number of throughholes.
16. A microphone according to claim 15, wherein the throughholes
allow sound waves to reach the diaphragm from a back-side of the
substrate.
17. A microphone according to claim 1, further comprising
electronic circuitry that produces a signal in response to
diaphragm movement.
18. A microphone according to claim 17, wherein the electronic
circuitry is formed direct or indirectly on the substrate.
19. A microphone comprising: a substrate; a diaphragm; support
means for movably coupling the diaphragm to the substrate, the
support means including carrier means for fixed coupling with the
substrate and suspension means for movably coupling the diaphragm
to the carrier means and spacing the diaphragm from the carrier
means; and insulator means for electrically isolating the diaphragm
and the substrate.
20. A microphone according to claim 19, further comprising means
for capacitively coupling the substrate and the diaphragm to form a
fixed plate and a movable plate of a variable capacitor.
21. A microphone according to claim 19, further comprising means
for allowing sound waves to reach the diaphragm from a back-side of
the substrate.
22. A microphone according to claim 19, further comprising means
for producing a signal in response to diaphragm movement.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 11/113,925 entitled MICROMACHINED MICROPHONE
AND MULTISENSOR AND METHOD FOR PRODUCING SAME filed on Apr. 25,
2005 in the names of John R. Martin, Timothy J. Brosnihan, Craig
Core, Thomas Kieran Nunan, Jason Weigold, Xin Zhang (Attorney
Docket No. 2550/A47). This application is also a
continuation-in-part of U.S. patent application Ser. No. 11/366,941
entitled PACKAGED MICROPHONE WITH ELECTRICALLY COUPLED LID filed on
Mar. 2, 2006 in the names of Kieran Harney, John R. Martin,
Lawrence Felton (Attorney Docket No. 2550/A88), which claims
priority from U.S. Provisional Patent Application No. 60/708,449
entitled MICROPHONE WITH PREMOLDED TYPE PACKAGE filed on Aug. 16,
2005 in the names of Lawrence Felton, Kieran Harney, and John
Martin (Attorney Docket No. 2550/A74). This application also claims
priority from U.S. Provisional Patent Application No. 60/760,854
entitled SUPPORT APPARATUS FOR MICROPHONE DIAPHRAGM filed on Jan.
20, 2006 in the names of Timothy J. Brosnihan, Xin Zhang, Craig
Core, and Jason W. Weigold (Attorney Docket No. 2550/A97). The
above-referenced patent applications are hereby incorporated herein
by reference in their entireties.
[0002] This patent application may also be related to one or more
of the following listed United States patent applications, which
are owned by Analog Devices, Inc. of Norwood, Mass., all of which
are hereby incorporated herein by reference in their entireties:
[0003] METHOD OF FORMING A MEMS DEVICE, naming Thomas Kieran Nunan
and Timothy J. Brosnihan, assigned attorney docket number 2550/A40,
filed Jan. 3, 2005, and having Ser. No. 11/028,249. [0004]
MICROPHONE WITH IRREGULAR DIAPHRAGM, naming Jason Weigold as
inventor, assigned attorney docket number 2550/A76, filed Aug. 23,
2005, and having Ser. No. 60/710,517, [0005] MULTI-MICROPHONE
SYSTEM, naming Jason Weigold and Kieran Harney as inventors,
assigned attorney docket number 2550/A77, filed Aug. 23, 2005, and
having Ser. No. 60/710,624, [0006] MICROPHONE SYSTEM, naming Kieran
Harney as inventor, assigned attorney docket number 2550/A78, filed
Aug. 23, 2005, and having Ser. No. 60/710,515, [0007] PARTIALLY
ETCHED LEADFRAME PACKAGES HAVING DIFFERENT TOP AND BOTTOM
TOPOLOGIES, naming Kieran Harney, John R. Martin, Lawrence Felton,
assigned attorney docket number 2550/A87, filed Jan. 24, 2006, and
having Ser. No. 11/338,439. [0008] MICROPHONE WITH ENLARGED
BACK-VOLUME, naming Kieran Harney as inventor, assigned attorney
docket number 2550/A89, filed Nov. 28, 2005, and having Ser. No.
60/740,169. [0009] MICROPHONE WITH PRESSURE RELIEF, naming Xin
Zhang, Michael W. Judy, Kieran P. Harney, Jason W. Weigold,
assigned attorney docket number 2550/B40, filed Jan. 17, 2007, and
having Ser. No. 60/885,314.
FIELD OF THE INVENTION
[0010] The invention generally relates to microphones and, more
particularly, the invention relates to support for microphone
diaphragms.
BACKGROUND OF THE INVENTION
[0011] Microelectromechanical systems ("MEMS," hereinafter "MEMS
devices") are used in a wide variety of applications. For example,
MEMS devices currently are implemented as microphones to convert
audible signals to electrical signals, as gyroscopes to detect
pitch angles of airplanes, and as accelerometers to selectively
deploy air bags in automobiles. In simplified terms, such MEMS
devices typically have a movable structure suspended from a
substrate, and associated circuitry that both senses movement of
the suspended structure and delivers the sensed movement data to
one or more external devices (e.g., an external computer). The
external device processes the sensed data to calculate the property
being measured (e.g., pitch angle or acceleration).
[0012] MEMS microphones are being increasingly used in a greater
number of applications. For example, MEMS microphones are often
used in cellular phones and other such devices. To penetrate more
markets, however, it is important to obtain satisfactory
sensitivity and signal to noise ratios that match more traditional
microphones.
[0013] MEMS microphones typically include a thin diaphragm
electrode and a fixed sensing electrode that is positioned
alongside the diaphragm electrode. The diaphragm electrode and the
fixed sensing electrode act like plates of a variable capacitor.
During operation of the microphone, charges are placed on the
diaphragm electrode and the fixed sensing electrode. As the
diaphragm electrode vibrates in response to sound waves, the change
in distance between the diaphragm electrode and the fixed sensing
electrode results in capacitance changes that correspond to the
sound waves. These changes in capacitance therefore produce an
electronic signal that is representative of the sound waves.
Eventually, this electronic signal may be processed to reproduce
the sound waves, for example, on a speaker.
[0014] FIG. 1 shows the general structure of a micromachined
microphone as known in the art. Among other things, the
micromachined microphone includes a diaphragm 102 and a bridge
electrode (i.e. backplate) 104. The diaphragm 102 and the backplate
104 act as electrodes for a capacitive circuit. As shown, the
backplate 104 may be perforated to allow sound waves to reach the
diaphragm 102. Alternatively or additionally, sound waves can be
made to reach the diaphragm through other channels. In any case,
sound waves cause the diaphragm to vibrate, and the vibrations can
be sensed as changes in capacitance between the diaphragm 102 and
the bridge 104. The micromachined microphone typically includes a
substantial cavity 106 behind the diaphragm 102 in order to allow
the diaphragm 102 to move freely.
[0015] Many MEMS microphones use a diaphragm that is anchored
completely around its periphery, similar to the head of a drum.
Such diaphragms can present a number of problems. For example, in
the presence of sound waves, such diaphragms tend to bow rather
than move up and down uniformly, as shown in FIG. 2A. Such bowing
can negatively affect the sensitivity of the microphone,
specifically due to the limited displacement of the diaphragm
causes by internal tension and the variation in distance between
portions of the diaphragm and the fixed sensing electrode. Also,
such diaphragms can suffer from sensitivity to stresses (e.g., heat
expansion), which can distort the shape of the diaphragm and can
affect the mechanical integrity of the diaphragm as well as the
sound quality produced by the microphone.
[0016] Some MEMS microphones have a diaphragm that is movably
connected with its underlying stationary member (referred to
hereinafter as a "carrier") by way of a plurality of springs. The
springs tend to enable the diaphragm to move up and down uniformly
(i.e., like a plunger), as shown in FIG. 2B.
SUMMARY OF THE INVENTION
[0017] In accordance with one aspect of the invention there is
provided a microphone having a substrate; a diaphragm assembly
supported by the substrate, the diaphragm assembly including at
least one carrier, a diaphragm, and at least one spring coupling
the diaphragm to the at least one carrier, the diaphragm being
spaced from the at least one carrier; and at least one insulator
between the substrate and the at least one carrier so as to
electrically isolate the diaphragm and the substrate.
[0018] In various alternative embodiments, the substrate and the
diaphragm may be capacitively coupled to form a fixed plate and a
movable plate of a variable capacitor. Each carrier may be coupled
to an insulator that is coupled to the substrate. The diaphragm may
be perforated and/or corrugated. The space between the diaphragm
and the at least one carrier may be in a nominal plane of the
diaphragm. The diaphragm may be stress isolated from the at least
one carrier. The at least one carrier may include a single unitary
carrier surrounding the diaphragm or may include a plurality of
distinct carriers. The at least one insulator may include an oxide.
The diaphragm assembly may include polysilicon. The at least one
insulator may be formed directly or indirectly on the substrate,
and the at least one carrier may be formed directly or indirectly
on the at least one insulator. The substrate may be formed from a
silicon layer of a silicon-on-insulator wafer. The substrate may
include a number of throughholes, in which case the throughholes
may allow sound waves to reach the diaphragm from a back-side of
the substrate. The microphone may include electronic circuitry that
produces a signal in response to diaphragm movement. The electronic
circuitry may be formed direct or indirectly on the substrate.
[0019] In accordance with another aspect of the invention there is
provided a microphone including a substrate; a diaphragm; support
means for movably coupling the diaphragm to the substrate, the
support means including carrier means for fixed coupling with the
substrate and suspension means for movably coupling the diaphragm
to the carrier means and spacing the diaphragm from the carrier
means; and insulator means for electrically isolating the diaphragm
and the substrate.
[0020] In various alternative embodiments, the microphone may
further include means for capacitively coupling the substrate and
the diaphragm to form a fixed plate and a movable plate of a
variable capacitor. The microphone may additionally or
alternatively include means for allowing sound waves to reach the
diaphragm from a back-side of the substrate. The microphone may
additionally or alternatively include means for producing a signal
in response to diaphragm movement.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The foregoing advantages of the invention will be
appreciated more fully from the following further description
thereof with reference to the accompanying drawings wherein:
[0022] FIG. 1 shows the general structure of a micromachined
microphone as known in the art;
[0023] FIG. 2A schematically shows the bowing motion of a drum-like
MEMS microphone diaphragm;
[0024] FIG. 2B schematically shows the plunging motion of a
spring-attached MEMS microphone diaphragm;
[0025] FIG. 3 schematically shows a MEMS microphone that may be
produced in accordance with illustrative embodiments of the
invention;
[0026] FIG. 4 schematically shows a plan view of the microphone of
FIG. 3 configured in accordance with illustrative embodiments of
the invention;
[0027] FIG. 5 shows a plan view photograph of a specific microphone
configured in accordance with illustrative embodiments;
[0028] FIG. 6 shows a close-up plan view picture of the spring
shown in FIG. 5;
[0029] FIG. 7 schematically shows a cross-sectional and partial top
view of a microphone configured in accordance with illustrative
embodiments of the invention, with the diaphragm in an unreleased
state; and
[0030] FIG. 8 schematically shows a cross-sectional and partial top
view of a microphone configured in accordance with illustrative
embodiments of the invention, with the diaphragm in a released
state.
[0031] In order to facilitate interpretation of black-and-white
reproductions of certain figures, various materials are identified
using the following legend: "S" indicates single-crystal silicon;
"O" indicates oxide; "P" indicates polysilicon; "M" indicates
metal; and "Pass" indicates a passivation material such as
nitride.
[0032] Unless the context otherwise suggests, like elements are
indicated by like numerals. Also, unless noted otherwise, the
drawings are not necessarily drawn to scale.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0033] In embodiments of the present invention, a MEMS microphone
includes a diaphragm assembly supported by a substrate. The
diaphragm assembly includes at least one carrier, a diaphragm, and
at least one spring coupling the diaphragm to the at least one
carrier such that the diaphragm is spaced from the at least one
carrier. An insulator (or separate insulators) between the
substrate and the at least one carrier electrically isolates the
diaphragm and the substrate. The carrier may be coupled directly to
the insulator and the insulator may be coupled directly to the
substrate; alternatively, one or more additional materials may
separate the insulator from the substrate and/or the carrier. With
the diaphragm and the substrate electrically isolated from one
another, the diaphragm and the substrate may be capacitively
coupled and therefore may be used as the two plates of a variable
capacitor in order to convert audible signals to electrical
signals.
[0034] FIG. 3 schematically shows an unpackaged MEMS microphone 10
(also referred to as a "microphone chip 10") in accordance with
illustrative embodiments of the invention. Among other things, the
microphone 10 includes a static backplate 12 that supports and
forms a variable capacitor with a diaphragm assembly including
diaphragm 14 (details of the connection of the diaphragm assembly
and the backplate 12 are discussed below). In illustrative
embodiments, the backplate 12 is formed from single crystal
silicon, the diaphragm assembly including diaphragm 14 is formed
from deposited polysilicon, and the insulator between the backplate
12 and the diaphragm assembly is formed from an oxide. In this
example, the backplate 12 is formed from the top silicon layer of a
silicon-on-insulator (SOI) wafer 20 and so rests on an underlying
oxide layer and a base silicon layer. To facilitate operation, the
backplate 12 has a plurality of throughholes 16 that lead to a
back-side cavity 18 formed through the underlying oxide layer and
the base silicon layer. The microphone 10 may be used or packaged
in such a way that sound waves reach the diaphragm 14 through the
back-side cavity 18 and throughholes 16.
[0035] Audio signals cause the diaphragm 14 to vibrate, thus
producing a changing capacitance. On-chip or off-chip circuitry
converts this changing capacitance into electrical signals that can
be further processed. It should be noted that discussion of the
microphone 10 shown in FIG. 3 is for illustrative purposes only.
Other MEMS microphones having similar or dissimilar structure to
the microphone 10 shown in FIG. 3 therefore may be used with
illustrative embodiments of the invention.
[0036] FIG. 4 schematically shows a plan view of a microphone 10
configured in accordance with illustrative embodiments. This
exemplary microphone 10 has many of the same features as those
shown in FIG. 3. Specifically, as shown, the microphone 10 includes
a substrate 20 with a plurality of carriers 22 (in this case, four
carriers) that support the diaphragm 14 via a plurality of springs
24. Unlike the diaphragm 14, each carrier 22 is fixedly coupled
with the substrate 20. In illustrative embodiments, a layer of
electrical insulator material (e.g., an oxide) couples each carrier
22 to the substrate 20 and electrically insulates each carrier 22
from the substrate 20.
[0037] Among other things, this arrangement forms an expansion
space 26 between at least one of the carriers 22 and the diaphragm
14. Therefore, if subjected to stresses, the diaphragm 14 can
freely expand into this space 26. Accordingly, under anticipated
stresses, the diaphragm 14 should not mechanically contact the
carriers 22 (such contact could degrade system performance).
[0038] FIG. 5 shows a plan view photograph of a specific microphone
10 configured in accordance with illustrative embodiments, while
FIG. 6 shows a close-up plan view picture of one spring 24 shown in
FIG. 5. It should be noted that the specific microphones 10 are
examples of various embodiments of the invention. Accordingly,
discussion of specific components, such as the shape and number of
springs 24, should not be construed to limit various embodiments of
the invention.
[0039] As shown, the microphone 10 has a circular diaphragm 14 and
four radially extending but circumferentially shaped springs 24
that form the space 26 between the carrier(s) 22 and the outer
peripheral edge of the diaphragm 14. In this example, the diaphragm
assembly includes a single unitary carrier 22 surrounding the
diaphragm 14. In addition to providing the noted expansion space
26, the springs 24 also should mitigate diaphragm bowing (i.e.,
when the diaphragm 14 is concave when viewed from its top) when
moved downwardly. Accordingly, because of this, the diaphragm 14
should move toward the substrate 20 in a more uniform manner than
prior art designs having no space 26 or springs 24. For example,
the diaphragm 14 may move upwardly and downwardly in a manner that
approximates a plunger. Accordingly, the diaphragm 14 should be
able to move up and down more freely, and more area of the inner
face of the diaphragm 14 should be usable to produce the underlying
signal.
[0040] FIG. 7 schematically shows a cross-sectional and partial top
view of a microphone 10 configured in accordance with illustrative
embodiments of the invention, with the diaphragm in an unreleased
state. This drawing schematically shows a number of features
discussed above, such as the space between the diaphragm 14 and the
substrate 20, as well as the space 26 between the diaphragm 14 and
the carrier 22. In this figure, the diaphragm is shown with an
underlayer of oxide, which is later removed in order to release the
diaphragm. FIG. 8 schematically shows a cross-sectional and partial
top view of a microphone configured in accordance with illustrative
embodiments of the invention, with the diaphragm in a released
state (i.e., with the underlayer of oxide removed).
[0041] In certain embodiments of the present invention, a
micromachined microphone may be formed from a silicon or
silicon-on-insulator (SOI) wafer. As known in the art, a SOI wafer
includes a top silicon layer, usually called the device layer, an
intermediate insulator (oxide) layer, and a bottom silicon layer
that is typically much thicker than the top silicon layer (e.g.,
approximately 650 microns). The top layer formed in either a
silicon or a SOI wafer may be relatively thin (e.g., approximately
10 microns thick) in some embodiments of the invention or may be
relatively thick (e.g., approximately 50 microns thick) in other
embodiments. In certain embodiments of the present invention, the
fixed sensing electrode (also referred to herein as a "backplate")
may be formed from the top silicon layer of the wafer, and the
diaphragm may be formed so as to be suspended above the top silicon
layer. Perforations may be formed in the fixed sensing electrode to
allow sound waves to reach the diaphragm from the bottom side of
the wafer. An insulating layer (e.g., an oxide layer) on the back
side of the top silicon layer, which may be the inherent oxide
layer of a SOI wafer or an oxide layer deposited on a silicon
wafer, may be used as an etch stop layer for controlling the
machining of the fixed sensing electrode.
[0042] An exemplary process for forming a micromachined microphone
from an SOI wafer involves etching trenches through the top silicon
layer of a blank SOI wafer into the intermediate oxide layer and
optionally through to the bottom silicon layer. The trenches are
then lined with an oxide material. A polysilicon material is then
deposited so as to fill the lined trenches and cover the top
silicon. The polysilicon material is patterned and etched to form
various sacrificial structures that will be removed later.
Additional oxide material is deposited. A polysilicon material is
deposited and patterned to form the diaphragm assembly including
the microphone diaphragm and suspension spring. Oxide is deposited,
and holes are etched to expose portions of the backplate and the
diaphragm assembly. Metal is deposited and patterned in order to
form an electrode for placing electrical charge on the diaphragm,
an electrode for placing electrical charge on the backplate, and a
plurality of bond pads. There may be electrical connections between
bond pads and the electrodes. Passivation layers (e.g., an oxide
layer covered by a nitride layer, which is a standard passivation
layer used for integrated circuitry) are then deposited. The
passivation layers are etched to expose the bond pad and to expose
the diaphragm. Photoresist material is deposited and then patterned
to expose a future pedestal area. The oxide at the future pedestal
area is then removed by etching. The remaining photoresist material
is removed, and the bottom silicon layer is optionally thinned from
approximately 650 microns to approximately 350 microns by any of
several methods including etching, grinding and polishing.
Photoresist material is deposited on the front side of the wafer so
as to form a photoresist pedestal. Photoresist material is also
deposited on the back side of the wafer and patterned to outline a
backside cavity. The backside cavity is formed by etching away a
portion of the bottom silicon layer to the intermediate oxide
layer. In an exemplary embodiment, the backside cavity after
packaging is approximately one cubic millimeter in volume. A
portion of the intermediate oxide layer within the cavity is
removed in order to expose the sacrificial polysilicon structures.
The sacrificial polysilicon structures are removed, e.g., by
exposing the polysilicon to XeF.sub.2 gas or another suitable
silicon etchant through the backside cavity. It should be noted
that the XeF.sub.2 gas may remove some of the exposed bottom
silicon layer, although this is generally undesirable. The oxide
behind the diaphragm is removed, e.g., by placing in an appropriate
liquid. Then, the front side photoresist material (including the
pedestal) is removed, e.g., in a dry etch (not a liquid). This
essentially releases the diaphragm and related structures. It
should be noted that the pedestal is used to support the delicate
microphone structures during release and may not be required in all
embodiments, particularly if vapor HF is used to remove the oxide
instead of a liquid.
[0043] An exemplary process for forming a micromachined microphone
from a regular silicon wafer involves depositing an oxide layer on
the silicon wafer. Then, a polysilicon material is patterned and
etched to form the diaphragm assembly. An oxide material is
deposited, and holes are etched to expose portions of the substrate
and the diaphragm assembly. Metal is deposited and patterned in
order to form bond pads and electrodes for placing charge on the
microphone diaphragm and backplate. There may be electrical
connections between the bond pads and one or more of the
electrodes. Passivation layers (e.g., an oxide layer covered by a
nitride layer, which is a standard passivation layer used for
integrated circuitry) are deposited. The passivation layers are
etched to expose the bond pads. A portion of the passivation layers
above the microphone structures is removed and the oxide over and
partially under the polysilicon structures is removed to form
resist pedestal areas. The back side of the silicon wafer is
optionally thinned from approximately 650 microns to approximately
350 microns by any of several methods including etching, grinding
and polishing the back side, and a layer of oxide is deposited on
the back side of the wafer. A photoresist material is deposited on
the front side of the wafer, and the oxide on the back side of the
wafer is patterned. A photoresist material is deposited and
patterned on the back side of the wafer, and trenches are etched
into the silicon wafer. The photoresist material is removed from
both the front side and the back side, and a new layer of
photoresist material is deposited on the front side for protection.
Cavities are then etched in the back side of the wafer using the
existing oxide as a hard mask. The trenches are then further etched
through the silicon layer to the resist pedestal areas of the
microphone region. The oxide exposed through the cavities is
removed, e.g., by exposing to HF gas. The remaining photoresist
material is removed from the front side of the wafer, thereby
releasing the microphone structures. Finally, borosilicate glass
may be aligned and anodic bonded to the back side of the wafer.
Microphone holes may be ultrasonically cut in the glass prior to
bonding.
[0044] It should also be noted that these described processes are
exemplary only. For any particular implementation, fewer,
additional, or different steps or processes may be utilized. In
some cases, materials different than those described may be
suitable for a particular step or process. It would be virtually
impossible to describe every combination and permutation of
materials and processes that could be employed in various
embodiments of the invention. Therefore, the present invention is
intended to include all such materials and processes including
suitable variations of the materials and processes described.
Furthermore, micromachined microphones of the types described above
may be formed on the same wafer along with an inertial sensor
and/or electronic circuitry and may be packaged in a variety of
form factors.
[0045] It should also be noted that the present invention is not
limited to any particular shape, configuration, or composition of
microphone diaphragm. The microphone may be, for example, round or
square, solid or perforated by one or more holes, and/or flat or
corrugated. Different diaphragm configurations might require
different or additional processes from those described. For
example, additional processes may be used to form holes or
corrugations in the diaphragm. In various embodiments described
above, the diaphragm assembly is polysilicon, but other materials
may be used.
[0046] It should also be noted that the present invention is not
limited to any particular type or number of springs for coupling
the diaphragm to the at least one carrier. Embodiments of the
present invention may use different types and numbers of springs.
For example, various embodiments of the present invention may use
spring types and configurations described in the related
application having attorney docket number 2550/B40, which was
incorporated by reference above.
[0047] It should also be noted that the present invention is not
limited to any particular type of insulator between the substrate
and the at least one carrier. In various embodiments described
above, the insulator is an oxide, but other types of insulators may
be used.
[0048] It should also be noted that the present invention is not
limited to any particular type of packaging. For example, various
embodiments of the present invention may use packaging techniques
described in the related applications having attorney docket
numbers 2550/A87 and 2550/A88, both of which were incorporated by
reference above.
[0049] Although the above discussion discloses various exemplary
embodiments of the invention, it should be apparent that those
skilled in the art can make various modifications that will achieve
some of the advantages of the invention without departing from the
true scope of the invention.
* * * * *